Two-piece drinking cups formed from sheets of a thermoformable plastics material (e.g., expanded polystyrene) are well known as evidenced by U.S. Pat. Nos. 3,658,615 and 3,854,583. the entire content of each being expressly incorporated hereinto by reference. In this regard, such two-piece cups are typically formed from a sidewall sheet of thermoformable plastics material whose ends are overlapped somewhat and bonded to one another to form a longitudinal sidewall seam. A bottom disc is then bonded to an inwardly turned annular bottom flange integral with the side wall to form a seal therebetween. See in this regard, U.S. Pat. No. 4,106,397, the entire content of which is expressly incorporated hereinto by reference.
One problem that is presented with conventional two-piece cups formed from thermoformable plastics materials includes the weakening of the lower annular bottom edge of the cup due to stresses that are induced by the heat and pressures involved in bonding the bottom wall disc to the inwardly turned side wall flange. Weakening of the annular bottom edge of the cup may, in turn, cause it to rupture thereby spilling the cup contents. The possibility of rupturing the bottom edge of the cup is especially acute if the cup is dropped some distance when filled with liquid. Thus, it would especially be desirable if a two-piece cup construction could be provided which minimize (if not eliminate entirely) the stresses at the bottom edge of the cup which are induced by the heat and pressures during the fabrication process. It is toward providing such a cup that the present invention is directed.
Broadly, the present invention is directed toward a two-piece cup whereby the bottom wall disc is bonded to an inwardly turned annular flange of the side wall by an upwardly and inwardly sloped transition wall. The transition wall allows the bottom wall disc to be bonded to the sidewall flange in such a manner that the annular bottom edge is substantially unaffected by the heat and pressures during the bonding process.
These and other aspects and advantages will become apparent form the following detailed description of the preferred exemplary embodiments thereof.